Voltage regulators are used for providing regulated voltage supply to electronic circuits. An example of a voltage regulator 100 is shown in FIG. 1. The voltage regulator 100 includes a p-type metal-oxide-semiconductor (PMOS) transistor 105, a device 110, and a capacitor 115. A load current flows through the device 110. The capacitor 115 is connected in parallel to the device 110. Examples of the device 110 can include an ammeter, a resistor or any current sensing device. The PMOS transistor 105 has a drain connected to an output terminal (VOUT), a gate, and a source connected to a voltage supply (VDD). A gate signal is provided to the gate to regulate the voltage being supplied to the output terminal.
In one embodiment, to sense and measure the load current supplied by the voltage regulator 100, a series resistive element can be placed in series with the device 110, and the voltage drop across the resistive element can be measured using an analog to digital converter (ADC). The maximum value of the drop across the resistive element is VMAX=VIN−VDS_MIN−VOUT. VDS_MIN is the dropout tolerable across the PMOS transistor 105. Hence, the resistance of the resistive element is determined to be RMAX=VMAX/IMAX.
Given RMAX is determined as above, VMAX can be measured through the ADC. However, for a load current I significantly lower than the current IMAX, the input to the ADC would be scaled down by the ratio of I/IMAX. The voltage measurement would be limited by ADC's resolution. The finite resolution of the ADC limits the minimum detectable current through this arrangement with a good accuracy.
In another embodiment, the load current can be sensed using a current mirror circuit by dumping the mirrored current on a resistor, and sensing the voltage developed across the resistor with an ADC. However, sensing of the load current is limited by the resolution of the ADC.
It is desired to have a voltage regulator that can sense the load current and overcome the effects of the ADC resolution.